Rob,
The following steps should get you where you want:
(i) Open up a new notebook and select from the menu items Format |Style
Sheet|ArticleClassic
(ii) Import a private copy of the style sheet by selecting from menu
items Format | Edit Style Sheet . The style sheet for your notebook
should appear.
(iii) Go to the Formulas and Programming Section of the style sheet
notebook and select the cell called Prototype for style
"DisplayFormula"
(iv) Open up the option inspector from menu item Format |Option
Inspector. The Option Inspector Dialog box should open.
(v) With the cell in Step (iii) selected, and the option values in the
Dialog box set on Selection, type in Lookup box:
CommonDefaultFormatTypes . The option inspector should take you to the
section: New Cell Defaults | CommonDefaultFormats ->{...}
(vi) Under the "Input" section change 'StandardForm' to
'TraditionalForm'
Now you should be able to type in your formulas with the default
traditionalForm fonts.
You can short cut this process by going directly to the Style Sheet and
clicking on the cell you selected in Step (iii) and opening up the cell
using the menu item: Format | Show Expression. All the options for that
cell will be displayed and you can simply add the option:
CommonDefaultFormatTypes->{"Input"->TraditionalForm}. Then click on
Show Expression and you are done.
Hope this helps,
Brian
ps: Paul Abbot is an expert on the use of TraditionalForm in his class
notebooks. Check out his responses to the mathgroup on this subject.